Currently, so-called “H-type” and “I-type” X-Y stage devices represent the principal configurations of stage devices as used in optical microlithography systems. In each of these types of stage devices, a “moving guide” extends between two “fixed” guides that extend parallel to each other in a first drive direction (e.g., X-direction). Each end of the moving guide is attached to respective slider that moves, in coordination with the other slider, along the respective fixed guide in the first drive direction. A “self-advancing stage” is mounted to a slider that moves along the moving guide in a second drive direction (e.g., Y-direction). The respective names of these stage devices are derived from the overall H- or I-shaped configurations, respectively, of the fixed and moving guides. Typically, the H-type stage device is used whenever stage movements in both the X-direction and Y-direction are “long-stroke” motions, and the I-type stage device is used whenever stage movements are “long stroke” in only one of the X- and Y-directions and “short stroke” in the other direction.
Recently, linear motors have made their debut as stage-movers in H-type and I-type stage devices. At least one respective linear motor is provided for each of the X-axis and Y-axis movements of the stage. Use of linear motors has allowed the stage devices to have relatively simple, compact, and low-mass construction, with efficient operation.
If H-type and I-type stage devices as summarized above were to be used in certain conventional charged-particle-beam (CPB) microlithography apparatus as reticle stages and/or substrate (wafer) stages, certain problems would arise, as follows. In such stage devices both the “actuator” (moving portion) and “stator” (stationary portion) of the linear motor of the self-advancing stage move relative to the stators of the linear motors associated with the fixed guides. Unfortunately, despite the advantages (summarized in the preceding paragraph) of stage devices having such configurations, the stage devices exhibit magnetic-field fluctuations that degrade exposure accuracy. Magnetically shielding the linear motors is a conceivable countermeasure for these field fluctuations, but such a countermeasure tends to be excessively complex.
An alternative configuration of a stage device is a so-called “cross-shaped” stage device, in which two respective parallel fixed guides are provided in the X-direction and in the Y-direction. Between the fixed guides are respective moving guides that intersect with each other in a cross configuration. The moving guides are mutually slidable relative to the fixed guides, and a stage is mounted to the intersection of the moving guides. In this configuration (as in the H- and I-type configurations summarized above) each linear motor comprises an array of permanent magnets (typically constituting the “stator”) and an “armature” coil (typically constituting the “actuator”). If the permanent magnets (which generate magnetic fields exhibiting relatively large fluctuations during operation) are secured to a stationary base and used as stators for both X-direction and Y-direction motion, and the armature coils (which generate magnetic fields exhibiting relatively small fluctuations during operation) are used as actuators, then magnetic-field fluctuations during exposure can be reduced somewhat compared to a converse configuration of stators and actuators. However, in the center of the cross-shaped stage configuration, the H-type or I-type stage configuration nevertheless is present, resulting in a very large stage device overall, which is impractical.
Another alternative stage configuration utilizes a linear motor exhibiting two degrees of freedom of motion. In such a linear motor the actuator can move in two directions (typically the X-direction and Y-direction) relative to stators arranged widely in a plane. However, this type of linear motor has a special configuration and is expensive.
Disclosed in U.S. Pat. No. 5,760,564 is a stage device that uses air bearings and vacuum pads to provide pressurization (pre-load) sufficient to impart a limited range of motion of a movable table in the Z-direction. The vacuum pads and air bearings are mounted to a base. With this device, the mass of the movable table is borne on the base. Also, the pressurization mechanism is simple, which allows the device to have relatively low mass overall. However, in a vacuum, no pre-load is applied If it is desired to increase the rigidity of the stage, many air bearings must be used, resulting in excessive complexity of the stage device. Although it is conceivable for pressurization to be provided by magnetic-attraction force instead of a vacuum, such an approach is not suitable for use in a CPB microlithography apparatus in which magnetic-field fluctuations should be maximally suppressed.